This just started happening to me after the latest Roku software update. Previously, the voice search feature on my remote was working flawlessly for years. I have the RC392 remote. I've tried fresh batteries, restarting the Roku device and the remote (by removing and reinserting fresh batteries), I've checked my router channel (I've manually set it), I've checked my firewall, Ive checked the Roku temperatures using the advanced hidden Roku menu and it's fine ( I keep two fans on my Roku streaming stick ), and the wifi signal is excellent. This only started happening after the latest Roku software update.
We shouldn’t have to buy a new remote if it was working fine for years. If a software update broke this feature, Roku should really look into it and fix it!